MEMS device and method for making the same

Abstract

A microelectromechanical system device includes a substrate, a dielectric layer, an electrode, a surface modification layer and a membrane. The dielectric layer is formed on the substrate, and is formed with a cavity that is defined by a cavity-defining wall. The electrode is formed in the dielectric layer. The surface modification layer covers the cavity-defining wall, and has a plurality of hydrophobic end groups. The membrane is connected to the dielectric layer, and seals the cavity. The membrane is movable toward or away from the electrode. A method for making a microelectromechanical system device is also provided.

What is claimed is: 
     
       1. A microelectromechanical system (MEMS) device comprising:
 a substrate; 
 a dielectric layer being formed on the substrate, and being formed with a cavity that is defined by a cavity-defining wall; 
 an electrode formed in the dielectric layer; 
 a surface modification layer covering the cavity-defining wall, the surface modification layer having a plurality of hydrophobic end groups; 
 a membrane connected to the dielectric layer and sealing the cavity, the membrane being movable toward or away from the electrode; 
 a venting passage penetrating the membrane and the dielectric layer and being in spatial communication with the cavity; and 
 a seal sealing the venting passage so as to hermetically isolate the cavity from the outside environment. 
 
     
     
       2. The MEMS device as claimed in  claim 1 , wherein the surface modification layer is a self-assembled monolayer that has a plurality of head groups connected to the cavity-defining wall and the hydrophobic end groups respectively connected to the head groups, the head groups including silane or alkyl. 
     
     
       3. The MEMS device as claimed in  claim 1 , wherein the surface modification layer includes a high-dielectric material. 
     
     
       4. The MEMS device as claimed in  claim 1 , wherein the surface modification layer has a thickness ranging from about 10 Å to about 100 Å. 
     
     
       5. The MEMS device as claimed in  claim 1 , wherein at least one of the dielectric layer and the membrane is formed with a protruding bump in the cavity. 
     
     
       6. A method for making a microelectromechanical system (MEMS) device, the method comprising:
 forming a dielectric layer on a substrate, the dielectric layer having an electrode formed therein; 
 forming a cavity in the dielectric layer so that the electrode is disposed underneath the cavity, the cavity being defined by a cavity-defining wall of the dielectric layer; 
 forming a surface modification layer covering the cavity-defining wall, the surface modification layer having a plurality of hydrophobic end groups; and 
 sealing the cavity with a membrane, the membrane being connected to the dielectric layer and being movable toward or away from the electrode, 
 wherein sealing the cavity includes connecting a semiconductor wafer to the dielectric layer though fusion bonding, followed by thinning the semiconductor wafer into the membrane. 
 
     
     
       7. The method as claimed in  claim 6 , further comprising:
 prior to forming the surface modification layer, forming a removable feature on the dielectric layer outside of the cavity-defining wall such that the surface modification layer is formed to cover the removable feature and the cavity-defining wall; and 
 after forming the surface modification layer, removing the removable feature and the surface modification layer on the removable feature. 
 
     
     
       8. The method as claimed in  claim 7 , wherein forming the surface modification layer includes exposing the dielectric layer and the removable feature to a self-assembled precursor, the self-assembled precursor including a plurality of head groups that are bonded to the dielectric layer and the removable feature, and the hydrophobic end groups that are respectively connected to the head groups. 
     
     
       9. The method as claimed in  claim 8 , wherein the head groups include silane or alkyl. 
     
     
       10. The method as claimed in  claim 6 , wherein the surface modification layer includes a high-dielectric material. 
     
     
       11. The method as claimed in  claim 6 , wherein:
 forming the cavity includes forming a recess in the dielectric layer, the recess being in spatial communication with the cavity; and 
 sealing the cavity with the membrane includes
 forming an opening in the membrane, the opening being in spatial communication with the recess and cooperating with the recess to define a venting passage, 
 venting the cavity through the venting passage, and 
 sealing the opening so as to hermetically isolate the cavity from the outside environment. 
 
 
     
     
       12. The method as claimed in  claim 11 , wherein:
 during forming the removable feature, the removable feature covers the recess; and 
 during removing the removable feature and the surface modification layer on the removable feature, the removable feature on the recess is removed so as to expose the recess, and the surface modification layer being outside of the recess. 
 
     
     
       13. A method for making a microelectromechanical system (MEMS) device, the method comprising:
 forming a dielectric layer on a substrate, the dielectric layer having an electrode formed therein; 
 forming a cavity in the dielectric layer so that the electrode is disposed underneath the cavity, the dielectric layer having a cavity-defining wall that defines the cavity and a bonding wall that is outside of the cavity-defining wall; 
 forming a surface modification layer covering the bonding wall and the cavity-defining wall, the surface modification layer having a plurality of hydrophobic end groups; 
 removing the surface modification layer on the bonding wall; and 
 sealing the cavity with a membrane, the membrane being connected to the bonding wall and being movable toward or away from the electrode. 
 
     
     
       14. The method as claimed in  claim 13 , wherein removing the surface modification layer includes:
 covering the surface modification layer on the cavity-defining wall with a removable feature; 
 removing the surface modification layer on the bonding wall; and 
 removing the removable feature. 
 
     
     
       15. The method as claimed in  claim 14 , wherein covering the surface modification layer on the cavity-defining wall with the removable feature includes covering the surface modification layer on the bonding wall and the cavity-defining wall with a photoresist layer, followed by developing the photoresist layer to remove the photoresist layer on the bonding wall. 
     
     
       16. The method as claimed in  claim 13 , wherein forming the surface modification layer includes exposing the dielectric layer to a self-assembled precursor, the self-assembled precursor including a plurality of head groups that are bonded to the dielectric layer and the removable feature, and the hydrophobic end groups that are respectively connected to the head groups. 
     
     
       17. The method as claimed in  claim 13 , wherein:
 forming the cavity includes forming a recess in the dielectric layer, the recess being in spatial communication with the cavity; and 
 sealing the cavity with the membrane includes
 forming an opening in the membrane, the opening being in spatial communication with the recess and cooperating with the recess to define a venting passage, 
 venting the cavity through the venting passage, and 
 sealing the opening so as to hermetically isolate the cavity from the outside environment. 
 
 
     
     
       18. The method as claimed in  claim 17 , wherein:
 during forming the surface modification layer, the recess is covered by the surface modification layer; and 
 during removing the surface modification layer, the surface modification layer covering the recess is removed. 
 
     
     
       19. The method as claimed in  claim 13 , wherein the surface modification layer is prepared from one of octadecyltrichlorosilane (OTS), dodecyltrichlorosilane (DTS), perfluorodecyltrichlorosilane (FDTS), hexadecyltrichlorosilane (HTS), dimethyldichlorosilane (DDMS), and fluoro-octyl-trichloro-silane (FOTS). 
     
     
       20. The method as claimed in  claim 14 , wherein the surface modification layer is formed by exposing the removable feature and the cavity-defining wall to a self-assembled precursor which is one of a silane-based material, an alkyl-based material, and a combination thereof.